The celestial object 1998 KY26, cataloged as a dark comet, may be the lost Soviet spacecraft Phobos 1, according to research released by astrophysicists on Tuesday (22). Orbital models and light reflections match the geometry of the derelict probe, cutting trajectory residuals by 11% across 260 radar and astrometric measurements.

Researchers Adam Hibberd and Adam Crowl from the Initiative for Interstellar Studies, along with Abraham Loeb, professor of astrophysics at Harvard University and director of the Galileo Project, presented their findings in a preprint titled “Feasibility of the Phobos 1 Hypothesis for Dark Comet 1998 KY26” on the arXiv repository. The study suggests that instead of being a natural icy rock propelled by unseen gases, the 11-meter body might be an artificial relic wandering through interplanetary space since the late Cold War.

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Photometric modeling matches 1998 KY26 to Phobos 1 geometry

The research team compared a three-dimensional model of the Phobos 1 bus, complete with solar panels and cylindrical tanks, against eight observed light curves recorded from 1998 KY26. Their calculations revealed that solar radiation pressure acting on these reflective surfaces naturally reproduces the slight non-gravitational push detected in the object’s path. When applying this solar pressure model to 260 radar and astrometric data points, the discrepancy between predicted and observed positions dropped significantly without needing to invoke undetected rocket-like gas jets.

Toni Santana-Ros, an astronomer at the University of Alicante, led an observational study published on September 18, 2025, in Nature Communications, which redefined the physical parameters of the target. Santana-Ros stated that “We found that the reality of the object is completely different from what it was previously described as” after establishing its extreme rotation rate and reflective surface. The calculated spin pole in Ecliptic J2000 coordinates, derived from the Phobos 1 assumption, was placed at 151 degrees longitude and 11 degrees latitude.

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• Estimated diameter: 11 meters, with an uncertainty margin of 2 meters
• Rotation period: 5.35 minutes along its axis
• Surface albedo: 52%, reflecting sunlight at an uncommonly high rate for an asteroid
• Residual reduction: 11% improvement across astrometric tracking records
• Observational baseline: 260 astrometric and radar points analyzed in the model
• Fitted curves: 8 separate photometric light curves aligned with the probe structure

Can Hayabusa2 confirm the identity of 1998 KY26 in 2031?

A definitive answer regarding the artificial nature of 1998 KY26 rests on an encounter planned by the Japan Aerospace Exploration Agency (JAXA). The Japanese spacecraft Hayabusa2, which previously collected 5.4 grams of surface material from asteroid Ryugu in 2019 and returned the capsule to Earth in December 2020, is currently navigating an extended exploration mission. Following a flyby past asteroid Torifune on July 5, 2026, the probe is scheduled to rendezvous with and attempt a landing on 1998 KY26 in July 2031.

Loeb addressed the expectations for that mission, noting that “Our prediction is that instead of an iceberg, Hayabusa 2’s cameras will reveal the`Made in the U.S.S.R.’” Referring to the historical resistance met by novel scientific ideas, Loeb also quoted German theoretical physicist Max Planck, who stated that “Science advances one funeral at a time.” The encounter in 2031 would represent the first time an active interplanetary spacecraft reaches a celestial body roughly 10 meters wide.

Chronology of Phobos 1 and observations of 1998 KY26

The Soviet probe Phobos 1 was originally designed to explore Mars and its largest moon, but human error cut the mission short only two months after its launch. The object designated 1998 KY26 was later located a decade later by ground-based instruments, and an earlier astrodynamics paper by Hibberd, Crowl, and Carlos Gómez de Olea Ballester in May 2026 first explored the orbital overlap between the lost spacecraft and the supposed asteroid.

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• July 7, 1988: The Soviet Union launches the Phobos 1 spacecraft toward Mars
• September 2, 1988: Ground controllers lose contact with Phobos 1 after a faulty command transmission
• May 28, 1998: The Spacewatch survey discovers the celestial body 1998 KY26
• September 18, 2025: Nature Communications publishes revised physical dimensions for 1998 KY26
• September 21, 2026: Authors submit the comparative feasibility paper to the arXiv archive
• July 2031: Hayabusa2 arrives at 1998 KY26 for close-range optical imaging and touchdown

Debate over 1998 KY26 and dark comet acceleration models

The classification of dark comets covers small Solar System bodies that display non-gravitational acceleration while showing no visible coma or tail. Precedents for human-made debris behaving like natural bodies have occurred before; in 2020, the Pan-STARRS telescope detected the object 2020 SO accelerating under solar radiation pressure, which scientists later identified as the Centaur upper stage of NASA’s 1966 Surveyor 2 lunar mission.

Disagreement remains within the astronomical community regarding the mechanisms acting on 1998 KY26. Mainstream planetary scientists propose that the non-gravitational acceleration of the body can be accounted for naturally by the Yarkovsky effect, a thermal force caused by uneven solar heating on an 11-meter rotating rock, without requiring artificial origin or outgassing. The paper by Hibberd, Crowl, and Loeb remains an unreviewed preprint on arXiv, leaving the origin of 1998 KY26 unresolved until close-up photographs are captured during the July 2031 rendezvous.